I looked at this thread a few weeks ago before I started studying for the GRE. I had very limited time to prepare since I decided to put my grad school application (M.S. Nuclear Engineering) in at the last minute.
Background: I bought the 5 lb. Manhatten Prep Study Problems book and worked through the majority of it in 3 weeks. I only hit on areas that I thought would be particularly troublesome (particularly the verbal).
Practice Exams:
Manhatten Free Exam : 159 Q / 161 V
PowerPrep 1 : 165 V / 164 Q
I took both of these test the week before I took my GRE.
Actual GRE: 165 Q / 160 V
From my experience, the PowerPrep practice exam felt much more like the actual GRE. During my GRE, I felt like I did much better on the verbal than I actually did, and I felt much worse about the quantitative. For me, I think it came down to the fact that I did not have tons of time to go back over my quantitative sections which made me feel uncertain of my performance, but at the end of the day I was fairly confident in most of my answers in the quantitative section. Overall, I cannot complain about my performance when I had limited hours to study. Given that I wanted at least 160 V and 165 Q, I guess I can honestly say I reached my absolute minimum goal which feels pretty good considering I didn't have the optimal study time/approach.
If I had to recommend an optimal method of studying, I would say that it is important to take as many practice exams as you need in order to feel comfortable with the time constraints. I think I could have benefited from a couple more practice exams in order to get my timing right (especially in the quantitative). At the end of the day, there wasn't a single question on the actual GRE quantitative that I didn't think I could solve, but there were a couple of questions that I just didn't have the right amount of time to devote to.
With the verbal, I think it is possible to do very well on sentence completion problems if you take the time to go over vocabulary. This is where the Manhatten book really helped since I its sentence completion practice problems were much more difficult than the actual exam. If I could do this all over again, I would take the time to go over more of the other verbal practice sections. I think it is very easy to get overconfident with the passage reading comprehension questions, and this is where I think I lost the most on my verbal score.
Overall: If you have very limited time to study (Study Time << 100 hours), then it is still very possible toreach a reasonable goal.
